This invention relates generally to a breathing method and apparatus for supplying air to a user having a lower partial pressure of oxygen (PO.sub.2) than the ambient air so as to simulate elevated altitude.
Persons who ordinarily function at a near-sea-level altitude frequently experience headache, shortness of breath, nausea, sleeplessness, and reduced endurance during the initial days at higher altitude, e.g. above 7,500 feet. These factors are, in large part, attributable to the diminishing amount of oxygen available as altitude increases. A typical situation involves a sea-level resident who occasionally takes a skiing weekend above 7,500 feet. As altitude increases, oxygen availability diminishes, thus requiring the person to breathe deeper in an effort to supply sufficient oxygen to his bloodstream. The partial pressure of oxygen (PO.sub.2) at 7,500 feet is only 75% (of the PO.sub.2 at sea level) and at 10,000 feet is only 65%. At 19,000 feet, the PO.sub.2 is only 50%, thus meaning that a unit volume of air at 19,000 feet contains only half as much oxygen as that same unit volume at sea level. Typically, after a few days at the higher altitude, the person will become acclimated and the aforementioned problems subside. Interestingly, evidence suggests that persons who experience high altitudes on a frequent and regular basis appear to maintain a certain degree of acclimation to the altitude and are considerably better able to avoid the aforementioned problems than infrequent visitors.